Along-shelf evolution and sea levels across the continental slope |
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| Institution: | 1. Institute of Oceanographic Sciences, now Proudman Oceanographic Laboratory, Bidston Observatory, Birkenhead L43 7RA, U.K.;1. Ecohydrology Research Group, Water Institute and Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada;2. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom;3. Department of Marine Biology, Charney School of Marine Sciences, University of Haifa, Mt Carmel, Haifa, Israel;1. Marine Science Program, University of South Carolina, Columbia, SC 29208, USA;2. Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA;3. Department of Earth & Ocean Sciences, University of South Carolina, Columbia, SC 29208, USA;4. College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA;5. Instituto de Investigaciones Cientificas, Universidad de Oriente, Boca de Rio, Isla de Margarita, Venezuela;6. Estacion de Investigaciones Marinas de Margarita, Fundacion La Salle de Ciencias Naturales, Punta de Piedras, Estado Nueva Esparta, Venezuela;1. Petroleum and Marine Research Division, Korea Institute of Geoscience & Mineral Resources, Daejeon 34132, South Korea;2. Department of Petroleum Drilling, Mongolian University of Science and Technology, Ulaanbaatar 14191, Mongolia;3. Department of Marine Environment and Bioscience, Korea Maritime and Ocean University, Busan 49112, South Korea;4. KIGAM Pohang Branch, Korea Institute of Geoscience & Mineral Resources, Pohang 37559, South Korea |
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| Abstract: | If wind-stress or a horizontal oceanic density gradient acts over an ocean basin with an adjacent continental shelf and slope, sea-surface slopes and currents are set up along the shelf and slope with a return flow in the ocean. The currents evolve from zero at blocked ends of the shelf and basin. Such evolution is essentially barotropic (even for baroclinic forcing) and is relevant to all flow adjustments after longshore changes of depth profile or forcing. The distance over which this evolution takes place is investigated analytically for simple geometries, and numerically for a range of shelf, slope and ocean widths, shelf/ocean depth ratios, frictional decay rates and oscillatory frequencies. A close correspondence is found with the decay distance (group velocity x decay time) for a lowest mode continental shelf wave, often exceeding 1000 km. This correspondence is used to interpret some published model calculations of shelf and slope currents or return flows resulting from wind-stress or alongshore pressure gradients.Where a slope current is evolving, coastal sea levels do not follow oceanic levels. Implications for coastal/oceanic level differences are discussed. Oceanic sea-level features of shorter scale than the above 1000 km (say) do not penetrate fully to the coast. However, coastal sea levels averaged around small islands without broad shelves well represent surrounding oceanic levels. |
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